An investigation identified national security risks posed by a crypto facility in Wyoming. It is near an Air Force base and a data center doing work for the Pentagon.
That's the big environmental issue with Bitcoin — other major cryptocurrencies have moved to proof-of-stake instead of proof-of-work, so they don't need vast quantities of energy, and when you stop using all that energy, the generators with the highest marginal cost shut down, which generally means coal or gas.
A few months ago I read up on how much energy is used in a bitcoin transaction compared to a VISA transaction, it was something like 10000 times more energy for a bitcoin transaction
Because the stakeholders become the new central bank, with all the same motivations and conflicts of interest. You end up with a "staked class" and an "unstaked class".
This is a contributing factor to why ethereum can be rolled back: because the stakeholders didn't like it.
Bitcoin essentially has the same thing though — it's just that the "staked class" is those who have built power-devouring ASIC facilities to compute lots of hashes. Get enough of them together, and you can roll back transactions via a Sybil attack, just as you can with organized action by stakeholders in a proof-of-stake cryptocurrency.